The present disclosure relates to an image processing device that renders an image, an image processing method used in the device, a computer program for implementing the method and a computer-readable recording medium recording the program.
A home entertainment system that not only executes a game program but also can reproduce a moving image has been proposed. In this home entertainment system, a Graphics Processing Unit (GPU) generates three-dimensional images using polygons (refer to e.g. U.S. Pat. No. 6,563,999). At this time, how to express light in a space as the rendering target is an important factor that determines an impression made on a person who views the image. For example, compared with a local illumination model, in which an illumination calculation is performed from only direct light to objects, a global illumination model, in which indirect light such as reflected light from wall and floor is also taken into consideration, allows generation of more realistic images.
In the global illumination model, a simulation is performed on how light generated from a light source is affected by the existence of objects. For example, the following methods are known: ray tracing methods, in which light propagation between a viewpoint and a light source is traced, and radiosity methods, in which mutual reflection of the energy of light on object surfaces is calculated to obtain the final energy distribution. Furthermore, as one kind of ray tracing method, there is a photon mapping method, in which light is modeled as virtual particles (commonly known as “photon”). In the photon mapping method, a large amount of photons generated from a light source are propagated while being made to act with objects stochastically and positions at which the photons finally reach object surfaces are recorded as a photon map. Then, an approximation calculation of the radiance to each pixel is performed from the distribution of the photons as viewed from a viewpoint (refer to e.g. Toward Practical Real-time Photon Mapping: Efficient GPU Density Estimation, M Mara, D Luebke, M McGuire, Proceeding I3D '13 Proceedings of the ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games, Pages 71 to 78).